New classes of immunolabels will be produced comprising large metal particles encapsulated within coordination shells of stabilizing ligands, the naturally occurring hollow protein apoferritin, or new synthetic inclusion molecules. The new probes will combine the high electron density, ease of visualization and range of sizes available with colloidal gold probes with the non-aggregation, high penetrating ability and sensitivities of smaller gold cluster immunoprobes. Methods are proposed for the chemically controlled growth of large bimetallic cluster complexes and colloids by catalytic metal deposition and ligand capping, and for the preparation of heavy atom cluster complexes and colloids within the hollow protein apoferritin. Syntheses are proposed for cage molecules with internal diameters from 5 nm to 20 nm, constructed using large gold cluster complexes, rigid rod supports and cross-linked flat plates. This unprecedented new class of large inclusion compounds with novel physical and chemical properties will be precursors to new imaging reagents, drug delivery systems and materials.